FUNCTIONS 225 



water in plant life is very different indeed from its role in 

 our own lives. To think of the absorption of water by 

 plants as corresponding in any way to the drinking of ani- 

 mals is to have an idea that is entirely wrong. It is also 

 wrong to think of the absorption of water and of solutes 

 as one and the same thing, even though they take place 

 together. The statement that " water from the soil carries 

 food up into the plant " is wrong in two places: the things 

 referred to on much of the way are not carried and they 

 are not food. 



We may think of the uses of water to the plant as at 

 least three : (1) It furnishes the medium by means of 

 which all movement inside of the plant is accomplished ; 

 without it, the protoplasm itself ceases its activity. (2) It 

 is itself used in food manufacture. (3) It causes the tur- 

 gidity of cells without which all the soft parts of a plant 

 collapse and wilt. (See page 75.) 



C. Respiration. — This function is not restricted to 

 leaves. It is a function of all living cells whether in plants 

 or in animals. In plants it occurs in stems, in roots, and 

 in seeds, especially in the cambium layers, and in all other 

 living cells as well as in those of the leaves. 



Respiration is that process whereby, principally through 

 the oxidation of food, energy is released. Without respi- 

 ration no work can be done by living things ; they quickly 

 perish. 



We are considering respiration under the subject of 

 leaves simply because it is principally through the leaves 

 that there occurs that exchange of gases which is the out- 

 ward evidence of respiration. It is through the leaves 

 that oxygen is principally received into the plant,' and 



